A methodology to estimate the patient diameter and thickness from thoracic and abdominal projection radiographs of adult patients

Patient dose management systems can be part of a department's quality management tools to estimate items such as the radiation burden in specific groups or list dose outliers for further follow up. Patient size information could improve both aspects, but is not generally available. A new metric is proposed to estimate patient size for thorax and abdominal projection radiography from parameters available in the dicom header and therefore accessible by dose management software. The tested hypothesis was that an attenuation metric, related to the ratio of detector air-kerma to incident air-kerma, inversely correlates with patient size. Such a metric was defined and then worked out for thorax and abdomen projection radiography. Input material consisted of the thorax or abdominal radiographs of 137 cases, completed with a recent CT scan as ground truth size. From the CT, the water equivalent diameter (WED) and water equivalent thickness (WET) were calculated. The correlation between the attenuation metric and the patient size was established separately for thorax and abdomen. Validation of the attenuation metric predicting the patient size was performed using extra sets of examinations on three more radiographic x-ray devices, with available CT scan. The attenuation metric had a good correlation (R ²) of 0.91 and 0.84 with the WED for thorax and abdomen respectively. The corresponding values for the WET were 0.89 and 0.78. Validation of the methodology on the devices with standardized exposure index in the dicom headers showed that the WED could be estimated within ±15% and the WET within ±30% for thorax and abdomen examinations. The ground truth and estimated size were found statistically equivalent. An attenuation metric based on dicom tags allows to estimate the patient size in projection radiography. This could now be implemented in patient dose management systems. (paper)